Hitherto, a carboxyl-modified latex has been employed as a binder for various fibers, asphalts, mortars, concretes or ceramics, for instance.
Various cationic polymer emulsions have been proposed, most of which, however, are not sufficiently effective to the use and the object thereof. Additionally, methods of preparing such polymer emulsions require complicated steps.
For example, there is known a method of copolymerizing a cationic monomer and other monomer(s) by seed polymerization in the absence of an emulsifier or in the presence of a cationic surfactant. According to the method, a seed latex is first prepared from the total amount of the cationic monomer and a part of the other monomer(s) and subsequently the remaining monomers are added to the resulting seed latex. Therefore, it is impossible to impart a large number of cationic groups to the surfaces of the latex grains by the said method so that stable polymerization is impossible (Japanese Patent Application Laid-Open Nos. 57-121048 and 59-142217).
Another method is known, where an ethylenic unsaturated monomer containing a cationic group-imparting agent selected from secondary amines, tertiary amines and quaternary ammonium salts is copolymerized with a part of copolymerizable ethylenic unsaturated monomer(s) in the presence of a chain-transfer agent in an aqueous medium to give a seed latex and thereafter the remaining monomers are added to the resulting seed latex to continue the copolymerization (Japanese Patent Application Laid-Open No. 61-261302).
The latter method is different from the former method. Specifically, according to the latter method, a cationic group-imparting agent is previously added to the monomer to be copolymerized for forming the seed latex so that the effect of imparting the cationic groups to the surfaces of the latex grains could be expected in some degree. However, the method requires the use of a chain-transfer agent in the step of preparing the seed latex, which is troublesome.